Saquinavir is an HIV protease inhibitor used in combination with ritonavir and other antiretroviral agents for the treatment of HIV-1 with advanced immunodeficiency. In 1995 it became the first protease inhibitor approved by the FDA, followed shortly by ritonavir in 1996, and remains in clinical use today due to a relatively benign adverse effect profile as compared to other antiretroviral therapies. While its efficacy was initially limited by exceptionally poor oral bioavailability (approximately 4%), its current indications require the co-administration of ritonavir, that increases the bioavailability and subsequent serum concentrations of saquinavir, thus dramatically improving antiviral activity. The HIV virus binds and penetrates the host cell. Viral RNA is transcribed into viral DNA via reverse transcriptase. Viral DNA enters the host nucleus and is integrated into the host DNA via integrase. The DNA is then transcribed, creating viral mRNA. Viral mRNA is translater into the gag-pol polyprotein. HIV protease is synthesized as part of the Gag-pol polyprotein, where Gag encodes for the capsid and matrix protein to form the outer protein shell, and Pol encodes for the reverse transcriptase and integrase protein to synthesize and incorporate its genome into host cells. HIV-1 protease cleaves the Gag-pol polyprotein into 66 molecular species, including HIV-1 protease, integrase, and reverse transcriptase. Saquinavir inhibits HIV-1 protease. This inhibition prevents the HIV virion from fully maturing and becoming infective. Using the lipid bilayer of the host cell, a virus is formed and released. The inhibition of HIV-1 protease prevents the necessary molecular species from forming, therefore preventing maturation and activation of viral particles. This forms immature, non-infectious viral particles, therefore, Saquinavir prevents the virus from reproducing.

Saquinavir Pathway References